The present invention relates generally to solar concentrators and more particularly to a solar concentrator that employs a turntable to permit the solar concentrators to be rotated about two orthogonal axes so as to reduce both cost and weight while providing improved performance.
Space-based satellites and solar orbit transfer vehicles frequently collect solar energy with solar concentrators to generate electrical energy and/or propulsive power. It is known in the art to employ imaging concentrators having a single reflective surface for this purpose. The known imaging concentrators typically are of very high optic quality, producing a highly focused beam of energy. These imaging concentrators, however, are relatively heavy and difficult to manufacture. Consequently, their incorporation into a satellite or vehicle platform tends to be costly, consuming both financial and payload capacity.
One alternative to imaging concentrators is a non-imaging concentrator, which employs both a primary concentrator and a secondary concentrator. The primary concentrator collects ambient light and provides a primary light beam that includes a focused portion and an unfocused portion. The secondary concentrator is situated across from the primary concentrator and includes a frusto-conical reflective surface. The secondary concentrator is configured such that the focused portion of primary light beam is transmitted through a hole in the secondary concentrator while the unfocused portion of the primary light beam is reflected back to the primary concentrator. The known non-imaging concentrators are typically lighter in weight, relatively easier to manufacture and less costly than similarly sized imaging concentrators, and as such, there use is more common. Several drawbacks, however, are known to exist.
The known arrangements typically employ a stationary boom having a gimbal mount for supporting the primary concentrator. The gimbal mount between the boom and the primary concentrator permits the primary concentrator to be rotated relative to the secondary concentrator. The gimbal mount, however, is rather costly and heavy.
Another drawback relates to the amount of sky that is visible to the primary concentrator and the type of primary concentrator that is used. Typically, the primary concentrator is constructed with either a 90xc2x0 solar offset angle or a 70xc2x0 solar offset angle. The 90xc2x0 solar offset angle permits 100% of the visible sky to be viewed but is relatively costly. The 70xc2x0 solar offset angle permits 85% of the visible sky to be viewed but is relatively less expensive.
Accordingly, an improved solar concentrator is needed which is relatively lighter in weight, less expensive, and which permits 100% of the visible sky to be viewed even with a primary concentrator having a 70xc2x0 solar offset angle.
In one preferred form, the present invention provides a non-imaging solar concentrator having a primary concentrator, a turntable, a first support structure, a second support structure and a drive mechanism. The primary concentrator is configured to concentrate ambient light into a primary beam. The turntable has a central aperture, which is sized to permit the primary beam to be transmitted therethrough, and a rotatable portion that is rotatable about a turntable axis. The first support structure couples the primary concentrator to a first side of the rotatable portion of the turntable and the second support structure is coupled to a second side of the rotatable portion of the turntable opposite the first side. The secondary concentrator coupled to the second support structure and includes a frusto-conical reflective surface and a beam aperture. The beam aperture is sized to permit a focused portion of the primary beam to be transmitted therethrough, while the frusto-conical reflective surface is configured to reflect an unfocused portion of the primary beam back to the primary concentrator. The drive mechanism is coupled to the rotatable portion of the turntable and is operable for rotating the rotatable portion of the turntable about the turntable axis.
In another preferred form, the present invention provides a method for positioning a non-imaging solar concentrator about a structure having a first axis, the non-imaging solar concentrator having a primary concentrator and a secondary concentrator, the primary concentrator being operable for concentrating ambient light into a primary beam, the secondary concentrator having a frusto-conical reflective surface and a beam aperture, the beam aperture being sized to permit a focused portion of the primary beam to be transmitted therethrough, the frusto-conical reflective surface being configured to reflect an unfocused portion of the primary beam back to the primary concentrator, the method including the steps of: providing a turntable having a rotatable portion and a central aperture formed therethrough, the rotatable portion having a rotational axis, the turntable being coupled to the structure such that the rotational axis is perpendicular to the first axis; coupling the primary solar concentrator to a first side of the rotatable portion of the turntable; coupling the secondary solar concentrator to a second side of the rotatable portion of the turntable; and selectively rotating the primary and secondary concentrators about the turntable axis and the turntable about the first axis to position the non-imaging solar concentrator in a predetermined orientation.